A compressor (unit) for compressing a certain process gas, and an expander (unit) for recovering power by utilizing an exhaust gas or the like after treatment may be arranged as a common train on the same shaft. In this case, a geared type (speed increasing gear type) compressor and expander have hitherto been conceivable. As shown in FIG. 2, for example, one train is composed of a compressor, an expander, and a drive unit (see Patent Document 1).
A line of machines (train) as shown in FIG. 2 is one in a chemical plant, and includes a drive unit (a steam turbine and a condenser) 100, a geared type (multistage) compressor 101, a motor/electric generator 102, and a geared type (multistage) expander 103. The individual units are coupled to one another, and mounted on a base frame, namely, a machine bed or table 104. A plurality of coolers, a condenser and other instruments indispensable to the operation of the plant are located below the machine table 104.
This line of machines can be started with the steam turbine as the drive unit 100, if steam is available. In this case, the motor/electric generator 102 takes over the drive of the line of machines after the synchronous rotational speed of the motor is reached. Only when a chemical process has been started, and an exhaust gas or exhaust steam from the process drives the expander 103, the expander 103 releases power. In this manner, some of the energy can be recovered.
The line of machines can also be started with the motor/electric generator 102. If steam is generated only after the start as a result of the ongoing chemical process, then the steam turbine, as the drive unit 100, further drives the line of machines.